Work for Citigroup, Nasdaq Could Be Fuel for Critics

WASHINGTON—Lawrence Summers, one of the leading contenders to be the next chairman of the Federal Reserve, is serving as a paid consultant to Citigroup Inc. and other financial institutions, roles that are likely to draw the focus of people who don't want him to get the high-profile job.

Mr. Summers, who remains on the Harvard University faculty after a tumultuous tenure as the school's president in the mid-2000s, also advises or...